1. Field of the Invention
The present invention is directed to fabrication of nanotube structures iii the form of nanobaskets by sputter deposition on porous substrates and their uses in various applications.
2. Prior Art
The potential of nanotechnology to provide new technological breakthroughs is the object of much current attention. Nanostructured materials have the potential for enhanced properties and efficiency improvements in virtually every area of science and technology through enhanced surface areas and quantum-scale reactions. This disclosure deals with the formation of novel nanoscale structures that have numerous potentially important applications.
An example of an application for nanotube structures is found in Assignee's U.S. Pat. No. 6,586,133 for “Nano-Battery Systems” issued Jul. 1, 2003. The patented disclosure is directed to nano-batteries and micro-batteries as well as their manufacture and use. Porous substrate technology is utilized wherein the substrate has a plurality of holes or pores that range in diameter between ten (10) micrometers to one (1) nanometer (nm).
Nanoscale or microscale deposition of particles by a sputtering process is also known. The process of sputtering may be defined as the ejection of particles from a condensed-matter target due to the impingement of energetic projectile particles. Operatively, the source of coating material, referred to as the target, is mounted opposite to the sample, in this case a porous substrate in a vacuum chamber. The most common method of generating ion bombardment is to backfill the evacuated chamber with a continual flow of gas and establish a glow discharge, indicating that ionization is occurring. A negative potential applied to the target causes it to be bombarded with positive-ions while the substrate is kept grounded. Impingement of the positive ion projectile results in ejection of target atoms or molecules and their deposition on the substrate.
One of the most useful characteristics of the sputtering process is its universality: virtually any material is a coating candidate. Sputtering systems assume an almost unlimited variety of configurations, depending on the desired application. DC discharge methods are often used for sputtering metals, while an RF potential is used for nonconducting materials. Ion-beam sources can also be used. Targets may be elements, alloys, or compounds, in either doped or undoped forms, and can be employed simultaneously or sequentially. The substrate may be electrically biased so that it too undergoes ion bombardment. A reactive gas may be used to introduce one of the coating constituents into the chamber, i.e. oxygen to combine with sputtered tin to form tin oxide (reactive sputtering). (Bunshah, Rointan F., “Handbook of Deposition Technologies for Films and Coatings: Science Technology and Applications”, 2nd Ed., Noyes Publications, 1994.)
A recent study of nanostructures fabricated by RF sputtering of barium strontium titanate (BST) on porous alumina substrates suggests that the sputtered material does not penetrate into pores. It has been observed that the deposited material preferentially gathers along the continuous circular edge of pore openings. (Elena D. Mishina et al., “Ferroelectric Nanostructures Sputtered On Alumina Membranes”, Physica E., 25 (2004) 35-41.
Another, similar study refers to this type of sputtered metal structure as “antidots.” (Vovk, A., et al, “Preparation, structural characterization, and dynamic properties investigation of permalloy antidot arrays.”, J. Appl. Phys., 97, 10.1506 (2005)) These differ from the structures claimed in this patent, in that the structures are not partially or complete capped, nor are they layered, and they are formed only from metals. Nor were the “antidots” used to assemble any sort of device.
Nanotubes and other nanostructures may be formed as large arrays, and in this form are often referred to as nanoporous or mesoporous structures. “Meso-porous” tin oxide structures have been created using surfactant templating techniques. (Qui, Limin, Ma, Jiming, et. Al., “Sythesis and Characterization of Mesostructured Tin Oxide with Crystalline Walls”, Langmuir, 14(9) 2579-2581, (1998)) The resultant material, however, consists of material containing irregular nanopores averaging about two (2) nm in size, without long-range order. It is markedly different from the invention claimed in this patent, which can be formed in large arrays of tunable pore sizes, which develops wall height as well as porosity, and which can be partially or completely capped to form the basket structure.
An additional unique aspect of the present invention is that it has been found to have a substructure of very small nanoparticles, i.e., the walls and caps of the basket are themselves composed of nanoparticles ten (10) nm and less in size. (P. Johnson and D. Teeters, Solid State Ionics (2006), in press) Numerous scientific studies attest to the importance of nanoparticulate grain size in performance characteristics of electronic, optical, and catalytic devices.
The use of sputter techniques to create partially or completely capped and/or layered nanotube structures is believed to be unique and opens a wide range of potential applications.
Accordingly, it would be desirable to produce a nanotube structure wherein at least one end of a nanotube is partially or completely closed or covered over so that the nanotube forms a nanobasket.
It would also be desirable to form a nanobasket by sputter deposition.
It would be desirable to form a large array of nanobaskets as a nanoporous architecture.
It would also be desirable to fabricate nanobaskets as a component of photovoltaic devices.
It would also be desirable to provide nanobaskets for use in battery systems.
It would also be desirable to provide nanobaskets for use as a catalytic device.
It would also be desirable to provide nanobaskets for use in optoelectronic devices.
It would also be desirable to provide nanobaskets for use in fuel cell assemblies.
It would also be desirable to provide nanobaskets for use as human bone mimics and tissue scaffolding.